1. Field of the Invention
The present invention relates to a paddle-wheel type flow meter for measuring flow rates of fluids, for example such as chemicals passing through a fluid-transport pipe, and more particularly to a paddle-wheel type flow meter in which a paddle wheel is rotatably driven by the fluids in substantially proportion to a flow rate of the fluids so that the flow rate is detected by counting the paddle tips of the paddle wheel as they pass across a transmission path of a light so as to intermittently block off the transmission path of the light.
2. Description of the Prior Art
Hitherto, a number of paddle-wheel type flow meters have been proposed.
In such conventional paddle-wheel type flow meters, a magnet is fixedly mounted on a paddle wheel which is rotatably mounted in a fluid-transport pipe. On the other hand, a magnetic head is fixedly mounted on a suitable site outside the fluid-transport pipe so as to count the number of revolutions of the paddle wheel, whereby the magnetic head issues a detection signal to a suitable electronic circuit so as to determine flow rates of the fluids passing through the transport pipe.
However, there are many adverse environments to the flow meter, for example such as those having a strong magnetic field and strong electromagnetic radiations. In such adverse environments, it is substantially impossible to expect normal operations of the magnetic head and the electronic circuit.
For example, during operation of an electrolytic apparatus for making caustic soda or sodium hydroxide, since a large amount of direct current is supplied to the apparatus, a strong magnetic field is formed around the apparatus.
Consequently, the need exists for a flow meter which will provide high reliability against such adverse environments so as to be steadily operated and to transmit a necessary flow-rate data to a suitable measuring station sufficiently remote from the adverse environments. However, such need is still not fulfilled.